This invention relates to a molding composition based on inorganic components which sets in the presence of water. More particularly, this invention concerns a composition comprising finely divided SiO.sub.2 or mixtures of finely divided SiO.sub.2 and Al.sub.2 O.sub.3, at least partially water soluble alkali silicate, alkaline earth silicate and/or ammonium silicate and/or their precursors from the corresponding oxides or hydroxides and amorphous, finely divided silicic acid. The invention further relates to a method for curing the molding compositions and the use of the molding composition for a particular purpose.
Curable aqueous molding compositions of the aforementioned type are known from German Offenlegungsschriften 32 46 602 A1, 32 46 604 A1 and 32 46 619 A1. For the production of molded articles, these compositions must be brought into molds and heated therein to at least 50.degree. C. and even up to 200.degree. C. After removal from the mold, further post-curing at temperatures of 80.degree. to 200.degree. C. may be required. The molded articles obtained have bending strengths of 15 to 30 MPa, compression strengths of 25 to 90 MPa, good vibration absorbing properties, relatively low shrinkage values and good dimensional stability under heat.
However, the molding compositions have the serious disadvantage that they require an elevated temperature of 50.degree. to 200.degree. C. and preferably of 60.degree. to 90.degree. C. for setting or polycondensing. In some cases, such an elevated temperature is required to attain at least a sufficient green strength for removal from the mold, after which renewed heating is required for post-curing.